1. Field of the Invention
The present invention relates to a polarized beam splitter for transmitting or reflecting a beam of incoming polarized light according to its plane of polarization.
2. Description of Background Information
Polarized beam splitters for transmitting one of two linearly polarized light beam, the polarization planes of which are at a right angle to each other and for reflecting the other are widely used as an optical splitter or a light propagation shifter disposed in optical application apparatuses. Such known polarized beam splitters are generally made of calcite or quartz, e.g. Wollaston prism, or may be formed by coating a prism with a dielectric material.
FIG. 1 illustrates the arrangement of a known polarized beam splitter using prisms. As shown, a polarized beam splitter 1 consists mainly of two right-angle prisms 1a and 1b with their base sides coated with layers of dielectric material and cemented to each other with an adhesive. The prism 1 is arranged so that the cemented area 1c (referred to as a dielectric layer hereinafter) allows a linearly polarized light vibrating vertically (referred to as an S polarized light) to pass through and a linearly polarized light vibrating horizontally (referred to as a P polarized light) to reflect. Also, the dielectric layer 1c is arranged at 45.degree. to the direction of incident of an incoming light A.
A beam of S polarized light A is introduced to pass through the prism 1 and through a quarter wave plate 2 prior to reflecting on a mirror 3. A reflected beam from the mirror 3 passes again through the quarter wave plate 2 and returns to the prism 1. The quarter wave plate 2 has a thickness equal to 1/4 the optical path length of a transmitting light, thus shifting the polarization of the linearly polarized light by 90.degree. through two pass actions. Accordingly, the reflected beam becomes a P polarized-light which is reflected by the dielectric layer 1c and propagates at a right angle to the incident direction of the incoming or S polarized light A, as shown in FIG. 1.
The disadvantages of such a prior art polarized beam splitter are however that its production and the assembly and adjustment of its components are troublesome and not suited for automated manufacturing. Also, its three-dimensional construction in principle is hardly reducible in size and particularly, in thickness.